onError method
Propagates errors to waiting requests when the original request fails.
Implementation
@override
void onError(DioException err, ErrorInterceptorHandler handler) {
final key = err.requestOptions.extra['_deduplicationKey'] as String?;
if (key != null && _pendingRequests.containsKey(key)) {
_pendingRequests[key]!.completeError(err);
_pendingRequests.remove(key);
}
handler.next(err);
}